Steam gasification of biomass in dual fluidized bed gasifiers: A review

Indirect or allothermal gasification of biomass in dual fluidized bed (DFB) gasifiers such as the Güssing gasifier or the biomass heatpipe reformer becomes particularly attractive for the conversion of biomass into hydrogen or any second generation fuel such as substitute natural gas (SNG), methanol or Fischer-Tropsch diesel fuel. Interconnected and indirectly heated DFB gasifiers produce syngas with H2/CO ratios of 2–3 and hydrogen concentrations even above 50 vol%(dry basis). Fluidized bed particles, the operating pressure, solids circulation rate and heat transfer coefficients determine the layout of these gasifiers. This article summarizes the state of the art with respect to layout and dimensioning of DFB gasifiers and reviews the impact of the steam equivalence ratio, fuel and bed material properties, char conversion, and combustion efficiency on cold gas efficiency and syngas quality of DFB gasifiers.